Overview

Facilities for async programming and communication.
go blocks are dispatched over an internal thread pool, which
defaults to 8 threads. The size of this pool can be modified using
the Java system property `clojure.core.async.pool-size`.
Set Java system property `clojure.core.async.go-checking` to true
to validate go blocks do not invoke core.async blocking operations.
Property is read once, at namespace load time. Recommended for use
primarily during development. Invalid blocking calls will throw in
go block threads - use Thread.setDefaultUncaughtExceptionHandler()
to catch and handle.

Public Variables and Functions

<!

function

Usage: (<! port)

takes a val from port. Must be called inside a (go ...) block. Will
return nil if closed. Will park if nothing is available.

<!!

function

Usage: (<!! port)

takes a val from port. Will return nil if closed. Will block
if nothing is available.
Not intended for use in direct or transitive calls from (go ...) blocks.
Use the clojure.core.async.go-checking flag to detect invalid use (see
namespace docs).

>!!

function

Usage: (>!! port val)

puts a val into port. nil values are not allowed. Will block if no
buffer space is available. Returns true unless port is already closed.
Not intended for use in direct or transitive calls from (go ...) blocks.
Use the clojure.core.async.go-checking flag to detect invalid use (see
namespace docs).

admix

alt!

macro

Usage: (alt! & clauses)

Makes a single choice between one of several channel operations,
as if by alts!, returning the value of the result expr corresponding
to the operation completed. Must be called inside a (go ...) block.
Each clause takes the form of:
channel-op[s] result-expr
where channel-ops is one of:
take-port - a single port to take
[take-port | [put-port put-val] ...] - a vector of ports as per alts!
:default | :priority - an option for alts!
and result-expr is either a list beginning with a vector, whereupon that
vector will be treated as a binding for the [val port] return of the
operation, else any other expression.
(alt!
[c t] ([val ch] (foo ch val))
x ([v] v)
[[out val]] :wrote
:default 42)
Each option may appear at most once. The choice and parking
characteristics are those of alts!.

alt!!

alts!

function

Usage: (alts! ports & {:as opts})

Completes at most one of several channel operations. Must be called
inside a (go ...) block. ports is a vector of channel endpoints,
which can be either a channel to take from or a vector of
[channel-to-put-to val-to-put], in any combination. Takes will be
made as if by <!, and puts will be made as if by >!. Unless
the :priority option is true, if more than one port operation is
ready a non-deterministic choice will be made. If no operation is
ready and a :default value is supplied, [default-val :default] will
be returned, otherwise alts! will park until the first operation to
become ready completes. Returns [val port] of the completed
operation, where val is the value taken for takes, and a
boolean (true unless already closed, as per put!) for puts.
opts are passed as :key val ... Supported options:
:default val - the value to use if none of the operations are immediately ready
:priority true - (default nil) when true, the operations will be tried in order.
Note: there is no guarantee that the port exps or val exprs will be
used, nor in what order should they be, so they should not be
depended upon for side effects.

alts!!

function

Usage: (alts!! ports & opts)

Like alts!, except takes will be made as if by <!!, and puts will
be made as if by >!!, will block until completed.
Not intended for use in direct or transitive calls from (go ...) blocks.
Use the clojure.core.async.go-checking flag to detect invalid use (see
namespace docs).

buffer

chan

Creates a channel with an optional buffer, an optional transducer
(like (map f), (filter p) etc or a composition thereof), and an
optional exception-handler. If buf-or-n is a number, will create
and use a fixed buffer of that size. If a transducer is supplied a
buffer must be specified. ex-handler must be a fn of one argument -
if an exception occurs during transformation it will be called with
the Throwable as an argument, and any non-nil return value will be
placed in the channel.

close!

function

Usage: (close! chan)

Closes a channel. The channel will no longer accept any puts (they
will be ignored). Data in the channel remains available for taking, until
exhausted, after which takes will return nil. If there are any
pending takes, they will be dispatched with nil. Closing a closed
channel is a no-op. Returns nil.
Logically closing happens after all puts have been delivered. Therefore, any
blocked or parked puts will remain blocked/parked until a taker releases them.

dropping-buffer

go

macro

Usage: (go & body)

Asynchronously executes the body, returning immediately to the
calling thread. Additionally, any visible calls to <!, >! and alt!/alts!
channel operations within the body will block (if necessary) by
'parking' the calling thread rather than tying up an OS thread (or
the only JS thread when in ClojureScript). Upon completion of the
operation, the body will be resumed.
go blocks should not (either directly or indirectly) perform operations
that may block indefinitely. Doing so risks depleting the fixed pool of
go block threads, causing all go block processing to stop. This includes
core.async blocking ops (those ending in !!) and other blocking IO.
Returns a channel which will receive the result of the body when
completed

map

function

Usage: (map f chs)
(map f chs buf-or-n)

Takes a function and a collection of source channels, and returns a
channel which contains the values produced by applying f to the set
of first items taken from each source channel, followed by applying
f to the set of second items from each channel, until any one of the
channels is closed, at which point the output channel will be
closed. The returned channel will be unbuffered by default, or a
buf-or-n can be supplied

merge

function

Usage: (merge chs)
(merge chs buf-or-n)

Takes a collection of source channels and returns a channel which
contains all values taken from them. The returned channel will be
unbuffered by default, or a buf-or-n can be supplied. The channel
will close after all the source channels have closed.

mix

function

Usage: (mix out)

Creates and returns a mix of one or more input channels which will
be put on the supplied out channel. Input sources can be added to
the mix with 'admix', and removed with 'unmix'. A mix supports
soloing, muting and pausing multiple inputs atomically using
'toggle', and can solo using either muting or pausing as determined
by 'solo-mode'.
Each channel can have zero or more boolean modes set via 'toggle':
:solo - when true, only this (ond other soloed) channel(s) will appear
in the mix output channel. :mute and :pause states of soloed
channels are ignored. If solo-mode is :mute, non-soloed
channels are muted, if :pause, non-soloed channels are
paused.
:mute - muted channels will have their contents consumed but not included in the mix
:pause - paused channels will not have their contents consumed (and thus also not included in the mix)

mult

function

Usage: (mult ch)

Creates and returns a mult(iple) of the supplied channel. Channels
containing copies of the channel can be created with 'tap', and
detached with 'untap'.
Each item is distributed to all taps in parallel and synchronously,
i.e. each tap must accept before the next item is distributed. Use
buffering/windowing to prevent slow taps from holding up the mult.
Items received when there are no taps get dropped.
If a tap puts to a closed channel, it will be removed from the mult.

onto-chan

onto-chan!

function

Usage: (onto-chan! ch coll)
(onto-chan! ch coll close?)

Puts the contents of coll into the supplied channel.
By default the channel will be closed after the items are copied,
but can be determined by the close? parameter.
Returns a channel which will close after the items are copied.
If accessing coll might block, use onto-chan!! instead

onto-chan!!

pipe

function

Usage: (pipe from to)
(pipe from to close?)

Takes elements from the from channel and supplies them to the to
channel. By default, the to channel will be closed when the from
channel closes, but can be determined by the close? parameter. Will
stop consuming the from channel if the to channel closes

pipeline

Takes elements from the from channel and supplies them to the to
channel, subject to the transducer xf, with parallelism n. Because
it is parallel, the transducer will be applied independently to each
element, not across elements, and may produce zero or more outputs
per input. Outputs will be returned in order relative to the
inputs. By default, the to channel will be closed when the from
channel closes, but can be determined by the close? parameter. Will
stop consuming the from channel if the to channel closes. Note this
should be used for computational parallelism. If you have multiple
blocking operations to put in flight, use pipeline-blocking instead,
If you have multiple asynchronous operations to put in flight, use
pipeline-async instead. See chan for semantics of ex-handler.

pipeline-async

Takes elements from the from channel and supplies them to the to
channel, subject to the async function af, with parallelism n. af
must be a function of two arguments, the first an input value and
the second a channel on which to place the result(s). af must close!
the channel before returning. The presumption is that af will
return immediately, having launched some asynchronous operation
(i.e. in another thread) whose completion/callback will manipulate
the result channel. Outputs will be returned in order relative to
the inputs. By default, the to channel will be closed when the from
channel closes, but can be determined by the close? parameter. Will
stop consuming the from channel if the to channel closes. See also
pipeline, pipeline-blocking.

promise-chan

Creates a promise channel with an optional transducer, and an optional
exception-handler. A promise channel can take exactly one value that consumers
will receive. Once full, puts complete but val is dropped (no transfer).
Consumers will block until either a value is placed in the channel or the
channel is closed, then return the value (or nil) forever. See chan for the
semantics of xform and ex-handler.

pub

function

Usage: (pub ch topic-fn)
(pub ch topic-fn buf-fn)

Creates and returns a pub(lication) of the supplied channel,
partitioned into topics by the topic-fn. topic-fn will be applied to
each value on the channel and the result will determine the 'topic'
on which that value will be put. Channels can be subscribed to
receive copies of topics using 'sub', and unsubscribed using
'unsub'. Each topic will be handled by an internal mult on a
dedicated channel. By default these internal channels are
unbuffered, but a buf-fn can be supplied which, given a topic,
creates a buffer with desired properties.
Each item is distributed to all subs in parallel and synchronously,
i.e. each sub must accept before the next item is distributed. Use
buffering/windowing to prevent slow subs from holding up the pub.
Items received when there are no matching subs get dropped.
Note that if buf-fns are used then each topic is handled
asynchronously, i.e. if a channel is subscribed to more than one
topic it should not expect them to be interleaved identically with
the source.

put!

Asynchronously puts a val into port, calling fn1 (if supplied) when
complete, passing false iff port is already closed. nil values are
not allowed. If on-caller? (default true) is true, and the put is
immediately accepted, will call fn1 on calling thread.
fn1 may be run in a fixed-size dispatch thread pool and should not
perform blocking IO, including core.async blocking ops (those that
end in !!).
Returns true unless port is already closed.

reduce

function

Usage: (reduce f init ch)

f should be a function of 2 arguments. Returns a channel containing
the single result of applying f to init and the first item from the
channel, then applying f to that result and the 2nd item, etc. If
the channel closes without yielding items, returns init and f is not
called. ch must close before reduce produces a result.

solo-mode

split

function

Usage: (split p ch)
(split p ch t-buf-or-n f-buf-or-n)

Takes a predicate and a source channel and returns a vector of two
channels, the first of which will contain the values for which the
predicate returned true, the second those for which it returned
false.
The out channels will be unbuffered by default, or two buf-or-ns can
be supplied. The channels will close after the source channel has
closed.

take

function

Usage: (take n ch)
(take n ch buf-or-n)

Returns a channel that will return, at most, n items from ch. After n items
have been returned, or ch has been closed, the return channel will close.
The output channel is unbuffered by default, unless buf-or-n is given.

take!

function

Usage: (take! port fn1)
(take! port fn1 on-caller?)

Asynchronously takes a val from port, passing to fn1. Will pass nil
if closed. If on-caller? (default true) is true, and value is
immediately available, will call fn1 on calling thread.
fn1 may be run in a fixed-size dispatch thread pool and should not
perform blocking IO, including core.async blocking ops (those that
end in !!).
Returns nil.

to-chan!!

toggle

function

Usage: (toggle mix state-map)

Atomically sets the state(s) of one or more channels in a mix. The
state map is a map of channels -> channel-state-map. A
channel-state-map is a map of attrs -> boolean, where attr is one or
more of :mute, :pause or :solo. Any states supplied are merged with
the current state.
Note that channels can be added to a mix via toggle, which can be
used to add channels in a particular (e.g. paused) state.